<label>分段数: <input type="number" id
="rectCount" value="20" min="1" max="100"
></label>
<div><span class="color-box" style="background
-color: rgba(255, 99, 132, 0.6);"></span
>黎曼和 (矩形)</div>
<div><span class="color-box" style="background
-color: rgba(75, 192, 192, 0.4);"></span
>定积分面积</div>
<p><strong>当前积分值:</strong> <span id
="integralValue">0.00</span></p>
<p><strong>黎曼和近似值:</strong> <span id
="riemannSum">0.00</span></p>
<p><strong>说明:</strong>
动态展示上限x从0到3时,函数f(x)=x²在[0
,x]上的定积分累积过程。蓝色半透明区域表示精确
的积分面积,红色半透明矩形表示黎曼和近似。</p
>
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const startBtn = document.getElementById('startBtn');